Users can access their MySQL databases by means of PHPMyAdmin while logged into the Plesk interface. After selecting the domain, click "Databases," select the database you wish to access, and push the "DB WebAdmin" button.
The server administrator can access any MySQL database from the command line. Log in to the server via SSH and use the command:
mysql -uadmin -p`cat /etc/psa/.psa.shadow` DATABASE_NAME